Formatting Hard Drive

I have just formatted an antiquated lap top and cannot remember what to do now that it is in DOS mode. I have a windows cd and want to reload it. Can anybody please tell me what to do in order to do this. Many thanks.

thanks for your help so far. After I have rebooted I simply get the A:> prompt, with no menu to select boot with cd rom. What have i done wrong? Typing setup just gives me the invalid command scenario!

Boot from the floppy and select the option start with CD- Rom support. At A: command prompt type E: and press enter. This should take you to the CD drive. At the E: prompt type 'setup'. Windows should then start the setup procedure from the CD.